1. Field of the Invention
The present invention relates to the production of fiber-reinforced metal matrix composite materials and, more particularly, to an improved process for fabricating such articles to provide a maximum fiber fill, as desired, and to impart reproducibility to fabrication from one article to the next.
2. Description of the Prior Art
The development of fiber-reinforced composite materials has received considerable attention in recent years. Progress has been made in the development of high strength, high quality fibers such as boron and silicon carbide-coated boron, for example, and their incorporation into a metal matrix such as aluminum, magnesium or titanium.
While the use of metal matrix fiber-reinforced composite tapes is well known to the manufacturer of composite materials, difficulties remain in the process of actually incorporating fibers into a fully densified metal matrix material to provide the desired end item. Much of the emphasis has centered on techniques for maintaining proper spacing and relative positioning between a multitude of the extremely small filaments prior to and during consolidation by hot press diffusion bonding. Additional focus has been on problems associated with fabricating large-sized composites. Some of these techniques have involved the preliminary fabrication of preforms, i.e., unconsolidated composites having the filaments in proper positional placement and in close association with metal matrix material.
In U.S. Pat. No. 3,419,952 to Carlson, there is disclosed a technique wherein grooves are provided in the surface of metal matrix sheets in order to position individual filaments prior to consolidation. In U.S. Pat. No. 3,443,301 to Basche et al, there is taught a method wherein individual filaments are provided with an overcoat of metal matrix material prior to hot pressing. In U.S. Pat. No. 3,606,667 to Kreider, metal matrix material is plasma sprayed onto filaments positioned on a backing foil to produce unconsolidated tapes which are subsequently diffusion bonded by hot pressing in a non-oxidizing atmosphere.
In U.S. Pat. No. 3,936,550 to Carlson et al, a fugitive binder (non-metallic adhesive bonding material which decomposes leaving substantially no residue upon heating at a temperature below the melting point of foil and filament) is used, in combination with foil deformation, to secure aligned filaments in place prior to consolidation.
In another practice using a fugitive binder, the binder is used to secure parallel filaments to a metal matrix foil sheet prior to stacking and consolidation. This technique typically utilizes a vacuum environment in the mold where subsequent hot pressing will occur to draw off (off-gas) the evaporated resin binder immediately prior to diffusion bonding of the preform. By virtue of the applied vacuum as well as the light pressure of flat caul plates at the ends of the stack, the filaments are held firmly between foils to thus maintain alinement as the resin is off-gassed. One of the problems inherent in this technique resides in the difficulty in achieving complete off-gassing. Since the gas being evacuated is, by virtue of physical constraints, required to travel along a lengthy path, i.e., between the foils in a direction parallel to and between adjacent filaments, complete removal of the resin binder gas has been problematical due to trapping or the like. In addition, this method presents problems with respect to the sequential hot step pressing of large composites since, as the fugitive binder is volatilized, the resulting gases are caused to travel through relatively cooler unconsolidated portions. This results in condensation and reformation into a new material which is no longer completely vaporizable at process conditions. The reliability of providing reproducible, uncontaminated, fully compacted composites by this prior fugitive binder technique has accordingly been low.